Research On Spin Transport Properties Of Superconducting Junctions Based On Topological Insulators

The discovery of topological insulator (TI) has attracted much attention in recent years. TIs have a bulk band gap and metallic surface states due to the time-reversal symmetry. A variety of phenomena have been predicted or confirmed after the discovery of TIs. It has been proved that the time-reversal symmetry may be broken when superconductor (SC) and ferromagnetic insulator (FI) touch the surface of a TI. The proximity effect gives superconductivity and ferromagnetism on the surface, and thus the variation of transport properties.Applying the method based on an extended Bogoliubiv-de Gennes (BdG) equation, we study the spin-polarized transport properties in the topological superconducting junction composed of FI and SC on a TI.Firstly, we investigate the spin-polarized transport features and the manipulation of the spin electron pairs entanglement in the FI/SC/FI topological superconducting junction on a narrow two-dimensional TI. It is shown that when the bias voltages and the spin-polarization of the two FIs are properly adjusted, in the energy window, the nonlocal Andreev reflection probability for one spin can reach 100%, while is thoroughly suppressed for the other spin, which means that pure spin entangled electron pairs can be obtained. More interestingly, in the energy window, nonlocal Andreev reflection probability in the antiferromagnetic configuration is zero, and thus the currents for the left and right leads are both zero, indicating 100%tunneling magnetoresistance with highly magnetic storage efficiency. The results can be experimentally demonstrated by measuring the tunneling conductance and the noise power. It could be the theoretical guidance for experimentally developing electronic device with the functions of quantum computation and magnetic storage of high efficiency.Secondly, we study the spin-polarized transport properties in a FI/FI/SC junction on the surface of a three-dimensional TI in arbitrary magnetic configuration. We investigate the variations of tunneling conductance with the incident angel of electron at different angel a between the directions of the two magnetic exchange fields and bias voltage V or with the angle a at different magnetic exchange energy m and V. Then, the tunneling magnetoresistance with the variation of α are studied. Lastly, we obtain the variations of tunneling conductance with Vat different m and a.